1. Field of the Invention
The present invention relates generally to multi emitter packages, and more particularly to surface mount packages having multiple emitters that are aligned to improve emission uniformity.
2. Description of the Related Art
In recent years, there have been dramatic improvements in light emitting diode (LED) technology such that LEDs of increased brightness and color fidelity have been introduced. Due to these improved LEDs and improved image processing technology, large format, full color LED video screens have become available and are now in common use. Large format LED displays typically comprise a combination of individual LED panels providing image resolutions determined by the distance between adjacent pixels or “pixel pitch”.
Outdoor display that may be intended for viewing from greater distances, can have relatively large pixel pitches and usually comprise discrete LED arrays. In the discrete LED arrays, a cluster of individually mounted red, green, and blue LEDs are driven to form what appears to the viewer as a full color pixel. On the other hand, indoor screens, which require shorter pixel pitches such as 3 mm or less, can comprise panels having a plurality of surface mount devices (SMD or SMDs) or other types of emitter packages, each of which defines a pixel. Each emitter package can carry red, green, and blue emitting LEDs whose emitted light combines to generate the desired wavelength or color of light.
Both indoor and outdoor displays are typically viewable across a substantial range of off-axis angles, such as up to 145° or even greater. The LEDs in some conventional emitter packages suffer from different emission characteristics at different viewing angles. The LEDs in these packages can be arranged in a cluster at or near the center of the package, and at different viewing angles the particular LED closest to the viewer may emit more prominently. For example, if the package were viewed at an angle such that the red LED was closest to the viewer, the red may emit more prominently than when the package is viewed directly. The same could be true for the blue and green LEDs. As a result, the color generated by the packages can be perceived as different depending on the viewing angle.
Conventional emitter packages can also suffer from a perceptible loss of color fidelity with increasing viewing angle. Additionally, the material of each emitter package and/or the material used to mount each of the LEDs within the packages may have reflective characteristics, which can further decrease color fidelity by creating unwanted light reflection and/or glare.
Emitter packages such as SMDs, whether containing integrated circuits or discrete components such as diodes or power transistors, can generate significant heat, particularly in high power devices. This heat typically needs to be dissipated to prevent premature component degradation or failure. This can require additional thermal management component to dissipate sufficient heat to maintain the operating temperature of the active circuit or junction side of the component below a target temperature (for example, 110° C. or below). Various thermal management strategies including conduction heat transfer are in common use. One conventional way of implementing conduction heat transfer for dissipating heat in an electronic package is to allow the heat to conduct away along the leads of the device. However, the leads often do not have sufficient mass or exposed surface area to provide effective heat dissipation. For example, high intensity LEDs that emit light principally in the visible part of the electromagnetic spectrum can generate significant amounts of heat that is difficult to dissipate using such conventional techniques.